在ViewPager中引用片段

Question

public static class MyPagerAdapter extends FragmentPagerAdapter {

    private static final String TAG = "MyPagerAdapter";
    private static HashMap<Integer, EventListFragment> mPageReferenceMap = new HashMap<Integer, EventListFragment>();

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return NUM_ITEMS;
    }

    @Override
    public Fragment getItem(int position) {
        Log.i(TAG, "getItem: "+position);
        int dateOffset = position-1;
        EventListFragment mFragment = EventListFragment.newInstance(dateOffset);
        mPageReferenceMap.put(position, mFragment);
        return mFragment;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        Log.i(TAG, "destroyItem: "+position);
        mPageReferenceMap.remove(position);
        super.destroyItem(container, position, object);
    }


    public EventListFragment getFragment(int key) {
        Log.i(TAG, "Size of pager references: "+mPageReferenceMap.size());
        return mPageReferenceMap.get(key);
    }
}

有没有什么好的方法来引用用eventlistfragment mFragment=eventlistfragment.newinstance（dateOffset）；创建的片段？或者我应该如何从我的活动（准确地说是从选项菜单）中刷新查看页中的片段？

Answer 1

我设法解决了。诀窍是在Activity中创建一个引用列表，而不是PagerAdapter。它是这样的：

List<WeakReference<EventListFragment>> fragList = new ArrayList<WeakReference<EventListFragment>>();

@Override
public void onAttachFragment (Fragment fragment) {
    Log.i(TAG, "onAttachFragment: "+fragment);
    if(fragment.getClass()==EventListFragment.class){
        fragList.add(new WeakReference<EventListFragment>((EventListFragment)fragment));
    }
}
public EventListFragment getFragmentByPosition(int position) {

    EventListFragment ret = null;
    for(WeakReference<EventListFragment> ref : fragList) {
        EventListFragment f = ref.get();
        if(f != null) {
            if(f.getPosition()==position){
                ret = f;
            }
        } else { //delete from list
            fragList.remove(f);
        }
    }
    return ret;

}

当然，您的片段必须实现getPosition()函数，但是我无论如何都需要这样的东西，所以这不是问题。

感谢Alex Lockwood对WeakReference的建议！